Content delivery systems manage selection and delivery of third-party content for a usually large number of third-party content providers. For each third-party content provider, a content delivery system maintains a set of criteria for selecting respective third-party content to deliver to client devices. The selection of third-party content items for delivery to client devices can involve multiple comparisons between keywords. The total amount of criteria maintained in association with the third-party content providers can impact the amount of memory resources and computational resources used by a content delivery system, and the amount of processing performed when handling requests for third-party content. Furthermore, as the number of third-party content providers or the number of respective criteria increases, selecting and distributing third-party content items in real time, responsive to requests for third-party content calls, becomes more challenging and more demanding in terms of memory and computational resources.